Because your TV is just outputting a 1920x1080 resolution screen stretched big which is very different from having a 5760x1080 setup where I can see practically all 180 degrees in front of you. (one screen is you looking forward, the left screen is you looking directly to the left and the right is you looking to the right all at the same time!)
Think of one screen as having only one of your eyes open. Eyefinity in this example would be opening your other eye. You can now see things that where not there before/ you had to move your single eye back and forth to see.
Edit: grammer and better examples. Edit again: better yet go onto youtube and look up some 3 screen eyefinity setups, the middle screen is what you see with your single screen and your 40" tv, while the other two screens give you some extra peripheral vision.
Going off of what "paperfox" said. I first thought that the eyefinity was just your original image just stretched across 3 monitors for one very large image. I thought, nice but not for me. I than watched some you-tube videos of people talking about the huge advantage you have over other people, being able to see more than them. A perfect example would be change your desktop resolution to 800x600. It's not very easy to navigate. That's why huge resolutions are so awesome. Now I have 2 more monitors on the way.
heh-heh. Wow...way to come at it, HIB. My wife still has trouble understanding this concept and no matter how much I explain it to her, she doesn't get it either.
You could have a 100" big screen, and you're still only getting a 1920x1080 resolution (1080P). What you see on that 100" TV, from left to right and top to bottom, are EXACTLY what you'd see on a 24" 1080P monitor. You get no further viewing angle/depth/width...whatever you want to call it...just because you're TV is bigger. You have the same exact number of pixels and thus the same image on either screen - a TV just has bigger pixels and the bigger they get, the more distorted your image will be.
EyeFinity, on the other hand, with three 1080P monitors (like my setup) is THREE 1080P monitors. The center monitor has what you'd normally see on your single monitor or your big TV. The side monitors, on the other hand, introduce peripheral vision on either side. It's NOT a single 1920x1080 view - it's 5760x1080. Yes...you have about 3/4" of bezel in between the monitors - whooptie doo. It has never affected me in any game I play. In fact, in the 10.3 drivers coming out next month, you'll be able to tell the Catalyst drivers how much bezel you have and it will adjust the image to "hide" that portion of the image behind the bezel instead of stretching it (maybe not the right term) across the monitors so you have a huge gap between them.
So, I'd say Paperfox and Anime are quite right and you, my friend, need to learn some etiquette and actually use EyeFinity before you spout off something you don't know about. I'd highly recommend looking at some YouTube videos of EyeFinity in action before you judge it being a POS. I, personally, can't imagine EVER gaming on a single screen again, regardless of how big it is.
A 40 inch tv will need to be at least 5 feet away from you or it will look like crap. I currently have eyefinity and previouly had a 42 hdtv hook up. I have even hooked up a 50 inch hdtv and there is no comparison. Eyefinity on 3 1080p monitors looks awesome and is a whole new level of gaming 10x better than a single hdtv or single monitor.
I picked up 3 1080p monitors acer model # h233h from cowboom for 107 bucks each.